Head Capsule Width Research Articles

Characterizing the sublethal effects of SmartStax PRO dietary exposure on life history traits of the western corn rootworm, Diabrotica virgifera virgifera LeConte.

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is an economically important pest of field corn (Zea mays L.) across the United States (U.S.) Corn Belt. Repeated use of transgenic hybrids expressing Bacillus thuringiensis (Bt) proteins has selected for field-evolved resistance to all current rootworm-active Bt proteins. The newest product available for WCR management is SmartStax® PRO, a rootworm-active pyramid containing Cry3Bb1, Cry34/35Ab1 [now reclassified as Gpp34Ab1/Tpp35Ab1] and a new mode of action, DvSnf7 dsRNA. Understanding the fitness of adult WCR after dietary exposure to SmartStax® PRO will identify potential impacts on WCR population dynamics and inform efforts to optimize resistance management strategies. Therefore, the objective of the present study was to characterize the effect of SmartStax® PRO dietary exposure on WCR life history traits. Adult WCR were collected during 2018 and 2019 from emergence tents placed over replicated field plots of SmartStax® PRO or non-rootworm Bt corn at a site with a history of rootworm-Bt trait use and suspected resistance to Cry3Bb1 and Cry34/35Ab1. Adult survival was reduced by 97.1–99.7% in SmartStax® PRO plots relative to the non-rootworm Bt corn plots during the study. Individual male/female pairs were fed different diets of ear tissue to simulate lifetime or adult exposure. Life history parameters measured included adult longevity, adult head capsule width, lifetime female egg production, and egg viability. Results indicate that lifetime or adult exposure to SmartStax® PRO significantly reduced adult longevity and lifetime egg production. Larval exposure to SmartStax® PRO significantly reduced WCR adult size. Results from this study collectively suggest that SmartStax® PRO may negatively impact WCR life history traits, which may lead to reduced population growth when deployed in an area with WCR resistance to Bt traits.

Biology and Morphometrics of Spodoptera litura (F.) on Castor

Biology and morphometrics of Spodoptera litura (F.) was studied by rearing it on castor under laboratory conditions. Morphology of life stages i.e., egg, larva, pupa and adult along with development period were observed. The width of head capsule was observed at each moult as 0.19, 0.25, 0.45, 0.71, 1.31 and 2.13 mm, respectively. The mean growth ratio of S. litura was observed as 1.64, which indicated that increase in head width in instars was only slightly varying from Dyar’s law.

The Mitochondrial Phosphatase PTPMT1 is Required for the Proper Growth Rate in the Red Flour Beetle, Tribolium castaneum.

Protein tyrosine phosphatase, mitochondrial 1 (PTPMT1) is a mitochondrial phosphatase that is highly conserved in animals. Functional analyses using knockout animals have revealed a variety of physiological roles of PTPMT1 in vertebrates and insects. However, because of the high lethality of knockout in these animals, the roles of PTPMT1 in the later postembryonic development remain relatively obscure. In the present study, using the RNA interference technique, we analyzed PTPMT1 functions in later larval stages of the red flour beetle, Tribolium castaneum. PTPMT1 was expressed in both anterior and posterior parts of the body constitutively without obvious fluctuations from the middle larval instar through pupation. The PTPMT1-knockdown larvae injected with PTPMT1 double-stranded RNA at the middle instar showed a prolonged larval period, which was mainly caused by an extra larval molt. On the other hand, the increase in adult body length was subtle in the PTPMT1-knockdown T. castaneum, and the head capsule width was smaller than that of the control animals at the same larval instar. The expression levels of genes encoded by the mitochondrial genome were reduced in PTPMT1-knockdown larvae, indicating that PTPMT1 plays an important role in mitochondrial function in T. castaneum, like in other species. By contrast, the expression levels of a juvenile hormone (JH)-biosynthetic gene and a JH-signaling gene were rather increased in the PTPMT1-knockdown larvae, which may have been caused indirectly by the reduction of larval growth rate. Altogether, these findings indicate that PTPMT1 is required for the proper growth rate via some mitochondrial physiological role in T. castaneum larvae.

Biology and biometric characteristics of Spodoptera frugiperda (Lepidoptera: Noctuidae) reared on different host plants with regard to diet.

The fall armyworm (FAW) Spodoptera frugiperda (J. E. Smith), native to the Americas, is a new invasive pest that was reported in India for the first time in May 2018. Being polyphagous, FAW can infest several different hosts and increase its population all year round. In this context, the present study was conducted under laboratory conditions to evaluate the biological parameters of FAW on four different hosts, Zea mays (maize), Gossypium hirsutum (cotton), Ricinus communis (castor) and Brassica oleracea var. botrytis (cauliflower), and a semi-synthetic diet. The shortest life cycle of 32.8 ± 0.52 days in males and 34.1 ± 0.43 days in females was observed on maize. Semi-synthetic diet was superior in terms of higher mean fecundity (1324.6 ± 61.21 eggs), larval weight (503 ± 0.02 mg), pupal weight (263 ± 0.01 mg) and adult female weight (128 ± 0.0mg) compared with natural hosts. Cotton was the least preferred host with a longer life cycle of 49.5 ± 0.50 days. Head capsule width and length were measured and the growth rate was validated using Dyar's rule. The mean width and length of the head capsule of first-instar larvae of FAW on different hosts was 0.35 ± 0.00 mm. The maximum width (2.76 ± 0.03 mm) and length (2.31 ± 0.03 mm) were observed in sixth-instar larvae grown on diet. The results of this study will be instrumental in understanding and formulating management strategies for FAW.

Effect of a short-cycle apple tree cultivar on oriental fruit moth (Lepidoptera: Tortricidae) development and larval behavior.

The oriental fruit moth, Grapholita molesta (Busch, 1916) has historically been a major problem in traditional apple-growing regions in Rio Grande do Sul and Santa Catarina; however, a lower occurrence of G. molesta has been observed in early variety ('Eva') than long cycles cultivar 'Gala' in Paraná State. The objective of this study was to evaluate the performance of immature and adult G. molesta in apple cultivars with short and long cycles, in addition to elucidating whether there is adaptive potential for development and fertility from the first generation to the fourth. The experimental treatments consisted of larvae fed 'Eva' and 'Gala' fruit and a commercial diet. Immature development time, head capsule width, longevity and reproductive parameters were compared across the treatments. The larvae of the fourth generation exhibited better performance than those of the first on 'Eva' and 'Gala'. Immature oriental fruit moth development occurred via four or five instars. A greater number of larvae with four instars occurred on 'Eva' than on 'Gala'. The head capsule width was narrower on 'Gala' than on 'Eva' for larvae with four instars. Females reared on 'Eva' also laid more eggs than those reared on 'Gala'. The larvae that were more adapted to the feeding conditions showed reduced cycles/instars, and the females exhibited better performance when new generations originated from the same substrate. The high fluctuation of G. molesta in 'Gala' orchards is not due to the nutritional condition of the fruits.

Biology and morphometric studies of beet armyworm, Spodoptera exigua (Hub.)

The study is mainly focused on the morphology of different stages i.e., egg, larvae, pupa and adult. The head capsule measurements (widest head width) were taken by use of Stereozoom binocular microscope. The beet armyworm undergoes 5 instars with a maximum and minimum head width of 0.26 ± 0.01 and 1.70 ± 0.05 mm respectively. The head capsule width of larval instars showed successive increase in a different ratio at each moult and did not follow regular geometrical progression (Dyar's law). Colour polymorphism was clearly observed in the fifth instar of S. exigua recording about 34 morphs with a range of colours i.e., green, black, pink and yellow being dominant with combination of colours and cannibalism also reported in the late instar stages. The total developmental period lasted for 32.38 ± 5.13 days.

Adult body size measurement redundancies in Osmia lignaria and Megachile rotundata (Hymenoptera: Megachilidae).

Metrics to assess relative adult bee body size have included both mass and morphometrics, but these metrics may not equally or reliably estimate body size for all bee species and in all situations, due to bee age, diet, and/or environment. Understanding the relationships between different metrics and possible redundancies in the information they afford is important but not always known. Body size measurements provide valuable data for interpreting research outcomes for managed solitary bees, including Osmia lignaria Say and Megachile rotundata F. (Hymenoptera: Megachilidae). Applied studies of these important and readily available U.S. crop pollinators focus on refining commercial management practices, and basic empirical studies in various scientific disciplines (from genomics to ecology) employ them as model systems to study solitary bees. To examine common metrics of body size, we measured head capsule width (HCW), intertegular distance (ITD), and fresh and dry weights of newly emerged adults of both species. Using linear and exponential models, we determined relationships between these body size metrics. For M. rotundata, linear models best described relationships between ITD and all other metrics, and between HCW and fresh and dry weights. For O. lignaria, linear models best fit relationships between all metrics except for fresh weight with both ITD and HCW, which were fitted better with exponential models. For both species, model fits were strongest when males and females were pooled. Depending on the study question, knowing that only one metric may reliably measure body size can simplify evaluations of O. lignaria and M. rotundata responses to artificial or environmental variables.

The impact of cassava and wheat flour substrates on the biological parameters and insecticide response in Tribolium castaneum (Herbst)

This study investigates the effect of flours obtained from cassava, wheat and their composite on larval morphology and developmental periods of Tribolium castaneum (Herbst) at ambient laboratory conditions (30 ± 5 °C and 75 ± 5% r.h.). Six different types of substrates were prepared from cassava and wheat flours with or without yeast. The main and interactive effects of substrate, concentration and exposure time on insecticide response of beetles to cypermethrin and DDVP were also evaluated. Six larval instars were recorded regardless of substrate type. Cassava flour without yeast and wheat flour with yeast produced larvae with the lowest and highest weights, body lengths and head capsule lengths and widths, respectively. Wheat flour with yeast and cassava flour without yeast produced beetles with the shortest and longest developmental periods, respectively. The morphological measurements and developmental periods of beetles reared on composite and wheat flours with yeast were not significantly different. All the main factors and their two-way interactions evoked a significant effect on beetles’ response to both insecticides. Beetles reared on cassava flour without yeast showed the least insecticide tolerance while the highest tolerance to cypermethrin and DDVP was observed in beetles reared on composite flour with yeast and wheat flour with yeast, respectively. In conclusion, substrate type considerably influenced the biological parameters and insecticide response of T. castaneum . Composite (wheat + cassava) flour could, however, increase insecticide tolerance of T. castaneum to cypermethrin but serve as a good substitute to wheat flour in rearing T. castaneum for scientific studies in the laboratories. • T. castaneum were reared on different substrates formulated from flours of wheat, cassava and their composite. • Beetles from cassava flour without yeast showed the least biological parameters and highest insecticide susceptibility. • Beetles from wheat and composite flours with yeast had the best biological parameters and highest insecticide tolerance. • Wheat flour could be substituted with composite (wheat + cassava) flour in rearing T. castaneum.

Seeking Alfalfa Resistance to a Rhizophagous Pest, the Clover Root Curculio (Sitona hispidulus F.).

Simple SummaryClover root curculio (CRC) is a root feeding pest of alfalfa and clover that reduces stand life and yield. With the cancellation of soil-active insecticides in alfalfa, CRC populations and associated root damage have increased. Current CRC management practices are limited in their ability to suppress larval feeding belowground. Here, we evaluated alfalfa populations for resistance to CRC larval feeding and development belowground, and adult leaf consumption and oviposition aboveground. Divergent selection in two alfalfa cultivars in field nurseries revealed that there is genetic variability in resistance to CRC larval feeding and that significant gains in resistance from selection can occur in as few as two or three cycles of selection. While larval development was similar across the alfalfa populations tested in the lab, one alfalfa population (NY1713) displayed an overall increase in nodulation resulting in significantly lower proportions of nodules being consumed by larvae. These results provide possible candidates and soil-less method for the development and evaluation of alfalfa cultivars that may reduce the impacts of CRC root feeding and that offer an additional option for CRC management. Since the cancellation of broad-spectrum soil-active insecticides in alfalfa (Medicago sativa L.) production, clover root curculio (Sitona hispidulus F.) (CRC) larval root damage has increased. Current CRC management practices are limited in their ability to suppress larval feeding belowground. First, we field screened developmental alfalfa populations for CRC damage. Subsequently, we developed a soil-less arena to observe nodule feeding and development (head capsule width) of larvae in the lab. This method was used to evaluate five alfalfa populations (two CRC-susceptible (control) and three CRC-resistant populations) against larvae. Further, one CRC-resistant population paired with its genetically similar susceptible population were tested against adult leaf consumption and oviposition in the greenhouse. Field screening revealed that the alfalfa populations selected for little or no larval root feeding damage were more resistant to CRC larval feeding than their corresponding unselected cultivars and significantly more resistant than populations selected for susceptibility. The development of a soil-less arena provided a useful method for evaluation of root-larva interactions. Although larval development was similar across susceptible and resistant alfalfa populations, one CRC-resistant population (NY1713) displayed overall increased nodulation and, thus, had a significantly lower proportion of nodules consumed by larvae. Adult feeding and oviposition aboveground were similar across all populations tested. These results provide possible candidates and screening method for the development and evaluation of alfalfa cultivars that may reduce the impacts of larval feeding and that offer an additional option for CRC management.

The Prepupa of Calindoea trifascialis (Lepidoptera, Thyrididae)

A prepupa is a non-feeding stage that occurs between the final feeding larval instar and the pupa. It is less common in Lepidoptera because most species pass relatively directly from feeding cessation to pupation. This paper describes the occurrence of such a stage in the thyridid moth, Calindoea trifascialis (Moore). The prepupa is primarily a functional designation based on attributes associated with an extended wandering phase. The distinctness of this stage was demarcated by observed changes in the integument at the transition point to the prepupa. It was also corroborated by morphometric comparisons of length and mass with the final feeding instar. Measures of head capsule width indicated a potential stage-based departure from the Brooks-Dyar rule. The model fit changed with the number of instars assigned to the life cycle and depending on whether the prepupa was considered as a distinct instar. In the latter case the deviation was marked; but with the prepupa excluded, the growth curves still hinted at compensatory adjustments to growth increment prior to the non-feeding period. Molting was cryptic as a result of the use of leaf shelters and the consumption of exuviae after ecdysis.

Detecting the Conspecific: Herbivory-Induced Olfactory Cues in the Fall Armyworm (Lepidoptera: Noctuidae).

The fall armyworm (FAW), Spodoptera frugiperda (Smith), is a polyphagous pest whose larval feeding threatens several economically important crops worldwide with especially severe damage to corn (Zea mays L.). Field-derived resistance to several conventional pesticides and Bt toxins have threatened the efficacy of current management strategies, necessitating the development of alternative pest management methods and technologies. One possible avenue is the use of volatile organic compounds (VOCs) and other secondary metabolites that are produced and sequestered by plants as a response to larval feeding. The effects of conspecific larval feeding on fall armyworm oviposition preferences and larval fitness were examined using two-choice oviposition experiments, larval feeding trials, targeted metabolomics, and VOC analyses. There was a significant preference for oviposition on corn plants that lacked larval feeding damage, and larvae fed tissue from damaged plants exhibited reduced weights and head capsule widths. All larval feeding promoted significantly increased metabolite and VOC concentrations compared to corn plants without any feeding. Metabolite differences were driven primarily by linoleic acid (which is directly toxic to fall armyworm) and tricarboxylic acids. Several VOCs with significantly increased concentrations in damaged corn plants were known oviposition deterrents that warrant further investigation in an integrated pest management context.

Characterizing the Relationship Between Western Corn Rootworm (Coleoptera: Chrysomelidae) Larval Survival on Cry3Bb1-Expressing Corn and Larval Development Metrics.

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a significant pest of field corn, Zea mays L. (Poales: Poaceae), across the United States Corn Belt. Widespread adoption and continuous use of corn hybrids expressing the Cry3Bb1 protein to manage the western corn rootworm has resulted in greater than expected injury to Cry3Bb1-expressing hybrids in multiple areas of Nebraska. Single-plant bioassays were conducted on larval western corn rootworm populations to determine the level of resistance present in various Nebraska counties. The results confirmed a mosaic of susceptibility to Cry3Bb1 across Nebraska. Larval development metrics, including head capsule width and fresh weight, were measured to quantify the relationship between the level of resistance to Cry3Bb1 and larval developmental rate. Regression and correlation analyses indicate a significant positive relationship between Cry3Bb1 corrected survival and both larval development metrics. Results indicate that as the level of resistance to Cry3Bb1 within field populations increases, mean head capsule width and larval fresh weight also increase. This increases our understanding of western corn rootworm population dynamics and age structure variability present in the transgenic landscape that is part of the complex interaction of factors that drives resistance evolution. This collective variability and complexity within the landscape reinforces the importance of making corn rootworm management decisions based on information collected at the local level.

Head Capsule Width, Body Weight and Length Measurements for Instar Determination in Mason Bee (Osmia cornifrons) Larvae

Osmia cornifrons is a cavity-nesting solitary species used as an apple pollinator in Korea. We collected Osmia spp larvae to examine potential correlations of larval stage. The head widths of from 1<SUP>st</SUP> to the 5<SUP>th</SUP> instar ranged from 0.4±0.1 to 1.3±0.3 mm, and growth rate of each instar was significantly highest between 1<SUP>st</SUP> and the 2<SUP>nd</SUP> instar. The fitness regression model for the head capsule width was analyzed. The head capsule width plotted against the number of instars resulted in a regression line of y=0.146x+0.551, R²=0.838. The body weights of the larvae increased with larval developmental stage, and the coefficient of variation of larval weights was high. However, the calculated regression line was y=5.122x² -12.154x+11.444, R²=0.900. The growth ratio of the larval length was clearly maximal between the 3<SUP>rd</SUP> and 4<SUP>th</SUP> instars, while that of 5<SUP>th</SUP> instar larvae was decreased. The calculated regression line is y=2.595x+0.472, R²=0.920. The result suggests that measurements of head capsule width, weight and length may be useful as a method to determine larval instar.

Biomorphic Characters of Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) on Maize in Pakistan

Fall armyworm, Spodoptera frugiperda belongs to order Lepidoptera and family Noctuidae, is becoming a serious threat in maize growing areas of the world. Firstly, it was reported from African countries and caused significant economic crop losses. Recently the pest has been reported from various areas of Pakistan and knowledge of biomorphic characters was important. By keeping in view, the current study was conducted. The study resulted that complete metamorphosis was observed. The eggs were white to yellow in colour and dome in shape with 2-3 days of the incubation period. The egg width and thickness were recorded as 0.22 and 0.19 mm, respectively. Six larval instars were recorded. The pinacula of each seta was well recorded on all larval instar but more conspicuous in the last instar (6th) as compared to others. Inverted Y line was present on larvae head that mostly differentiates this species from other reported Spodoptera species. First, second, third, fourth, fifth and sixth larval head capsule width was 0.18±0.02, 0.29±0.00, 0.50±0.01, 0.76±0.47, 1.10±0.13 and 1.98±0.12 mm, respectively. The length and width of the 6th instar larva were 26.98±2.93 and 3.90±0.00 mm, respectively. The total larval period was 15-20 days on maize leaves. Obtect pupa was whitish green. Male was short-lived than female. The pre oviposition, oviposition and post oviposition periods were 2-5, 2-4 and 4-6 days, respectively. The study will be proved fruitful for coming researchers and farmers to control this pest.

Morphometric Analysis of Larval Instar Stages of Reared Red Palm Weevil, Rhynchophorus Ferrugineus (Oliver, 1790), (Coleoptera:Curcolionidae)

This study was conducted to explore alternative morphometric characters that could be used to estimate the larval age of red palm weevil (RPW), Rhynchophorus ferrugineus. A total of 14 characters explored in the study. Morphological characters were measured using Image J software and data were analyzed using One-way analysis of variance (ANOVA), principal components analysis (PCA), and discriminant function analysis (DFA). One-way ANOVA excluded characters that are not different among instars, which were distal head band (DB), basal head band (BB), distal tail width (DT), tail ratio (TR), and head band ratio (HBR). All other characters were found to be significant at p &lt; 0.05. For PCA, cumulative variations of 88.7% from the first two principal components, evidenced by sharp decrease in slope of the scree plot, has resulted from high loadings in dorsal surface area (DSA), total surface area (TSA), ventral surface area (VSA), head capsule width (HW), body length (BL) ranging from 0.955 to 0.984. For DFA, only one function explained a canonical correlation of 0.986 with 94.9% variation, and Wilk’s Lambda statistics of (0.007). The highest character loadings were BL, DSA, and HW, and could be useful characters in distinguishing instar ages of RPW larvae.

Bionomics of slender burnished brass (Thysanoplusia orichalcea [Fabricius, 1775], Lepidoptera: Noctuidae) on potato (Solanum tuberosum L.) in Kashmir

A study on biology, morphometrics and geometrical progression of Thysanoplusia orichalcea was conducted on Solanum tuberosumunder laboratory conditions. Different stages viz., egg, larva, pupa and adult of T. orichalcea were observed for their duration and morphometric measurements. The pest depicted five larval instars and moultedfour times during the entire period. The average pre oviposition and oviposition period was observed to be 3.80 and 2.80 days respectively.Further, fecundity ranges between 381.0-400.0 with an average of 388.0 eggs. The mean incubation period was found to be 4.2 days. The average larval, pre pupal and pupal period was completed in 23.1, 1.4 and 9.5 days respectively. While mean adult longevity on S. tuberosum was 7.45 days. The total life cycle was completed in 41.0-51.0 days with an average of 45.65 days. Moreover, mean head capsule width of first, second, third, fourth and fifth larval instar was found to be 0.33, 0.54, 0.88, 1.46 and 2.24 mm respectivelywith Dyar’s ratio/ growth ratio of 1.63 mm. The expected head capsule width of first, second, third, fourth and fifth larval instar wasobserved as 0.33, 0.53, 0.86, 1.40 and 2.28 mm respectively.

Unexpected larval habit of Listronotus bonariensis (Coleoptera: Curculionidae) raises questions about population dynamics analysis and management

AbstractListronotus bonariensis (Kuschel) is a pest of agriculturally important graminaceous species, with mining larvae that kill the stems of the host plants. In this study, larval populations were measured in spring and summer in irrigated dairy grassland comprising Lolium perenne L. (cv. Nui) with and without the endophyte Epichloë festucae var. lolii Latch, M.J. Chr. and Samuels and Poa annua L.. Larvae were extracted from tillers taken from the swards of these two grass species and extracted from turves, and L. bonariensis population densities were estimated from tiller and turf larval counts on a m−2 basis. Over the study period, the total number of larvae and larval densities extracted from turves was on average 2× greater than indicated from tillers. In most seasons, larval densities from turves were significantly higher than those from the tillers, though there was no correlation between tiller and turf larval densities. Mean head capsule widths of larvae emerging from turf samples showed significant seasonal effects compared with tillers, while mean head capsule widths of all four instars were significantly greater when extracted from tillers compared with turves. There was a significant endophyte effect on head capsule widths of larvae collected in summer, but the effect was not consistent across instars or source. Conversely, no significant endophyte effect on head capsule width was found in spring populations from either tillers or turves. This study shows that in irrigated dairy pasture, a high proportion of L. bonariensis larvae can live externally of tillers, presumably among the organic matter around the base of grasses in irrigated dairy pasture, and that density estimates based only on tiller populations will have significantly underestimated actual numbers. Having a precise indication of larval population densities is essential when developing life tables or determining economic damage threshold levels.

Development of Dermestes tessellatocollis Motschulsky under different constant temperatures and its implication in forensic entomology

Dermestidae generally appears on dry corpses and carcasses, especially if mummified or skeletonized. They are forensically important insect species for estimating longer postmortem intervals (PMI). As they develop, Dermestidae larvae undergo multiple larval ecdyses; however, a lack of guidelines for determining the larval instar limits their forensic application. Herein, we explored how temperature impacts the development of Dermestes tessellatocollis Motschulsky, 1860 (Coleoptera: Dermestidae). At seven constant temperatures (16, 19, 22, 25, 28, 31, and 34 °C), the developmental time from egg to adult was 163.87 ± 9.19, 103.56 ± 3.02, 63.59 ± 2.88, 51.49 ± 2.74, 47.86 ± 3.01, 44.62 ± 4.65, and 41.80 ± 4.87 days respectively. Four morphological indexes, including head capsule width, pronotum width, mesonotum width, and body length, were taken in vivo at regular intervals to identify methods for larval instar determination in D. tessellatocollis. The acquired morphological data were used to simulate fitted curves and equations depicting the relationship between the four morphological indexes and instars. From the validation experiment, we could hardly determine a specific instar based on the morphological indexes. The combination of morphometric data (head capsule, pronotum, and mesonotum width) generated the classification accuracy at 100%, 87.5%, 85%, and 93% for the 1st, 2nd/3rd, 4th/5th, and 6th/7th instars, respectively. Nevertheless, the accuracy was unsatisfactory for application in forensic casework. This study provides fundamental development data for adopting D. tessellatocollis in minimum postmortem interval (PMImin) estimations; however, further studies are needed to improve the classification accuracy for the larval instar determination.

Development of immature stages of Heteronychus arator rugifrons (Fairmaire, 1871) (Coleoptera: Dynastidae), a major crop pest in Madagascar

Adults (black beetles), and to a lesser extent, larvae (white grubs), of Heteronychus arator rugifrons (Fairmaire) are major crop pests of cereals—particularly upland rice—in the central highlands of the island of Madagascar. Since the biology of this endemic subspecies is far less well understood than that of the African black beetle Heteronychus arator F., we undertook laboratory studies to determine the developmental durations of its immature stages at two temperatures, with measurements taken (body length and weight of all stages/instars, head capsule width of all larval instars). The mean immature stage development period was significantly shorter at 25°C (160.8 ± 11.60 d) than at 18°C (251.4 ± 11.93 d), mainly due to shorter egg incubation, L1 instar and pupal periods. Some morphological traits of immature stages confirmed that H. arator rugifrons is a distinct subspecies from H. arator. In particular, head capsule width was homogenous among larval instars, irrespective of the rearing temperature, with no overlap across instars. Head capsule width range was 1.04–1.52 for L1, 1.72–2.36 for L2, and 2.40–3.48 for L3. This information should be helpful in studies of population dynamics and economic threshold calculations with a view to management of this pest.

Restoration of susceptibility following removal of selection for Cry34/35Ab1 resistance documents fitness costs in resistant population of western corn rootworm, Diabrotica virgifera virgifera.

Management of the corn pest, western corn rootworm (WCR), Diabrotica virgifera virgifera (LeConte) (Coleoptera: Chrysomelidae), relies heavily on the planting of transgenic corn expressing toxins produced by the bacterium Bacillus thuringiensis (Bt). This has resulted in the evolution of resistance to all of the four commercially available Bt toxins targeting coleopteran insects. In this study, we evaluated the susceptibility of a Cry34/35Ab1-resistant WCR colony in seedling and diet toxicity assays after removal from selection for six and nine generations. In addition, female fecundity, egg fertility, adult lifespan, larval development, and adult emergence were evaluated in two Cry34/35Ab1-resistant and two susceptible WCR colonies to assess fitness costs. Susceptibility to Cry34/35Ab1 was restored in a colony removed from selection after six and nine generations based on diet toxicity assays and comparisons of relative survival, head capsule width, and dry weight in plant assays. Thus, pronounced fitness costs associated with resistance to Cry34/35Ab1 were documented by susceptibility being restored within six generations. In separate studies evaluating specific fitness costs, larval fitness when reared on isoline corn did not differ between resistant and susceptible colonies. However, beetles from susceptible colonies lived longer than resistant beetles which resulted in females from susceptible colonies producing significantly more eggs than resistant colonies, with no differences in egg fertility. The presence of a fitness cost that may contribute to the restoration of susceptibility to Bt has not been documented in other Cry3-resistant WCR populations and could have significant impact on the deployment of resistance management practices. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.